Stonehenge’s Avenue and Bluestonehenge Michael J. Allen1, Ben Chan2, Ros Cleal3, Charles French4, Peter Marshall5, Joshua Pollard6, Rebecca Pullen7, Colin Richards8, Clive Ruggles9, David Robinson10, Jim Rylatt11, Julian Thomas8, Kate Welham12 & Mike Parker Pearson13,* Stonehenge has long been known to form part of a larger prehistoric landscape (Figure 1). In particular, it is part of a composite monument that includes the Stonehenge Avenue, first mapped in 1719–1723 by William Stukeley (1740) who recorded that it ran from Stonehenge’s northeast entrance for over a kilometre towards the River Avon, bending southeast and crossing King Barrow Ridge before disappearing under ploughed ground. He also noted that its initial 500m-long stretch from Stonehenge was aligned towards the midsummer solstice sunrise. Archaeological excavations during the 20th century revealed that the Avenue consists of two parallel banks with external, V-profile ditches, about 22m apart. The dating, phasing and extent of the Avenue, however, remained uncertain. Its length could be traced no closer than 200m from the River Avon (Smith 1973), and the question of whether the Avenue’s construction constituted a single event had not been entirely resolved (Cleal et al. 1995: 327). Our investigations were part of a re-evaluation of Stonehenge and its relationship to the River Avon in 2008–2009, involving the re-opening and extension of trenches previously dug across the Avenue during the 20th century and digging new trenches at West Amesbury beyond the then-known limit of the Avenue. The result of this work was the discovery of a new henge at West Amesbury, situated at the hitherto undiscovered east end of the Avenue beside the River Avon. Inside that henge were found the remains of an earlier circle of stoneholes, formerly holding small standing stones, that has come to be known as ‘Bluestonehenge’. Two of the aims of the Stonehenge Riverside Project (SRP) were to establish whether the Avenue was built in more than one phase, and whether it actually reached the river, thereby addressing the theory that Stonehenge was part of a larger complex linked by the river to Durrington Walls henge and its newly discovered avenue, two miles upstream (Parker Pearson & Ramilisonina 1998; Parker Pearson et al. 2007). A further opportunity to investigate the Stonehenge Avenue arose in August 2013 when Wessex Archaeology excavated along the line of the decommissioned A344 road (constructed in the 1760s) that runs across the Avenue close to Stonehenge, with the aim of examining the condition of the Avenue and its ditches where it lay under the road (Wessex Archaeology 2015). This paper describes the most significant results from these 21st-century investigations along different parts of the Stonehenge Avenue and at West Amesbury henge, beside the River Avon. These were primarily along that part of the Avenue nearest Stonehenge (the solstice-aligned section of the Stonehenge Avenue) and at West Amesbury henge (within which is the former stone circle of 1 Allen Environmental Archaeology, Redroof, Green Rd, Codford, Wilts, BA12 0NW, UK 2 Faculty of Archaeology, Leiden University, Postbus 9514, 2300 RA Leiden, The Netherlands 3 Alexander Keiller Museum, Avebury, Wilts, SN8 1RF, UK 4 Department of Archaeology & Anthropology, University of Cambridge, Cambridge, CB2 3DZ, UK 5 Chronologies, 25 Onslow Road, Sheffield, S11 7AF, UK 6 Department of Archaeology, University of Southampton, SO17 1BF, UK 7 Historic England, 37 Tanner Row, York, YO1 6WP, UK 8 School of Arts, Languages & Cultures, University of Manchester, M13 9PL, UK 9 School of Archaeology & Ancient History, University of Leicester, LE1 7RH, UK 10 School of Forensic and Investigative Sciences, University of Central Lancashire, PR1 2HE, UK 11 16 Carr Road, Sheffield, S6 2WZ, UK 12 Department of Archaeology, Anthropology & Forensic Science, Bournemouth University, BH12 5BB, UK 13 UCL Institute of Archaeology, 31-34 Gordon Square, London WC1H 0PY, UK * Author for correspondence (Email: [email protected]) Bluestonehenge). Other investigations at the Avenue bend (500m northeast of Stonehenge; see Figure 5) are not included. The solstice-aligned section of the Stonehenge Avenue Richard Atkinson’s 1956 trench C48 (Cleal et al. 1995: fig. 178; SRP’s Trench 45) was re-opened and extended by hand 2m southwards to form a trench 4m x 26m (Figure 2). Atkinson’s photographs and section drawing revealed gullies within the Avenue that were interpreted as periglacial fissures (Cleal et al. 1995: 311) but their orientation parallel with the Avenue’s axis suggested the possibility that they were, in fact, artificial features, such as palisade trenches or footings for timbers laid in order to slide stones or sledges. On excavation in 2008, the gullies were confirmed to be surprisingly large and deep periglacial stripes, consisting of 0.5m deep and 0.4m wide fissures in the chalk bedrock (Figure 3), filled with clean, beige- coloured silt formed from an admixture of material derived from weathered or soliflucted chalk and reworked aeolian loessic silt deposits (Figure 4). They were considerably more substantial than the much smaller periglacial stripes (less than 0.2m wide and 0.1m deep) observed in other trenches beside the Avenue and at its bend, and considerably deeper than many others regularly recorded on the chalk more widely. They are entirely natural features that formed long before human activity in the Holocene. Earth resistance and fluxgate magnetometer surveys reveal linear anomalies running along the line of the Avenue, but cart-tracks running within it on the same axis are partly responsible for these geophysical linear anomalies (see also Darvill et al. 2012a: 83–4). These cart-ruts are only 0.08–0.18m deep, far shallower than the periglacial fissures, and are visible in the magnetometer surveys as the thin linear anomalies that dominate, especially near the Avenue bend. Stronger and wider anomalies near the start of the Avenue are more likely produced by the periglacial fissures. Periglacial stripes are frost-heave cryoturbation features primarily created by in situ freeze–thaw alteration of the chalk, combined with ice removal and solution of loose chalk material (West 1968: 73–4). On the Wiltshire chalk, these cryoturbation structures are found on slopes of generally greater than 2° but less than 5° (Williams 1973: 26–7; French 1976): the ‘general result is … of parallel gullies orientated in a downhill direction’ (Evans 1968: 14), and usually in a slight diagonal direction across the slope. The presence of extraordinarily large and closely spaced periglacial stripes within the Avenue is possibly explained by the presence of natural ridges on either side of the concentration of stripes, and a natural dishing of the area between. These stripes are not water-cut channels per se, but freeze–thaw channels which, once created, will have encouraged water movement down them. Freeze–thaw action within and between the two natural ridges will have accentuated periglacial cryoturbation and infill processes, thus enlarging the periglacial stripes. The ridges can be seen in Hawley’s photograph of his excavations outside Stonehenge’s northeast entrance (Hawley 1925: plate X; Cleal et al. 1995: fig. 184) and are visible as earthwork features running for 150m or so from the Heel Stone (Field et al. 2012: fig. 10) but not as far as the Avenue bend (Figure 5). These two natural ridges (each c.6m wide) were initially thought to result from differential weathering of the chalk surface, with those areas beneath the Avenue banks being protected to a greater degree. However, the ridges are far wider than the banks, which are up to 4.3m wide and stand only 0.1m high. As is the case with the bank and ditch enclosing Stonehenge (Cleal et al. 1995: fig. 48), such a degree of differential preservation of bedrock can only be achieved at the base of a very substantial bank, thus certainly not possible in the case of the Stonehenge Avenue’s insubstantial banks. There is no evidence for the natural ridges having being formed by cultivation outside the Avenue’s banks reducing the soil/chalk level, thus leaving the Avenue banks and underlying chalk artificially raised. There is no evidence of any plough-soil or plough-marks up against the sides of the Avenue within Trench 45; field banks and lynchets have been mapped in this landscape but much further away (Field et al. 2012). Nor is there any evidence of ploughing – ancient or modern – in another trench (Trench 44), just 50m away; furthermore, absence of ploughing is indicated in that trench by the sharp boundary of sarsen chips in its shallow soil (Parker Pearson 2012: 251). Finally, differential plough erosion is not a persuasive explanation for formation of the narrow hollow between the two natural ridges. The 2008 excavation across the Avenue in Trench 45 revealed few features. One of these was a small tree-hole cutting through the ancient land surface. Another was an irregular, shallow pit (or a pair of pits) lying within the Avenue. This pit went undetected during the 1956 excavation but was found in 2008 to be 1.7m E–W x 1.4m N–S x 0.23m deep, containing sarsen and bluestone chips as well as a small red deer antler pick at its base. The pit was partly covered by the edge of the Avenue bank but whether this was primary upcast or secondary material from re-cutting of the Avenue ditch could not be determined. The slightly ‘dirty’ appearance of the upcast chalk in this part of the bank suggests the latter. Many of the 3,535 small flakes and fragments of sarsen and 71 bluestone fragments in Trench 45 came from two patches of buried soil beneath the Avenue banks, confirming that dressing of Stonehenge’s stones was carried out prior to the Avenue’s construction (see also Pitts 1982: 101–2; Hawley 1925: 23).